The background of the invention will be set forth in three parts.
1. Field of the Invention
The present invention relates to optical recognition and, more particularly, to a hand-held probe for reading bar codes.
2. Prior Art
With regard to the art of optical code scanning, a number of devices are known which read printed bar codes optically and obtain digital information therefrom.
Berler, et al., in U.S. Pat. No. 3,731,064, disclose a binary code which is scanned by a hand-held reader comprising a lens, light source, and photoelectric sensor. The code comprises lines of a predetermined width and spaces which may be one of three different widths. Two widths signify 0 or 1; the third is an equalizing bit which makes each five-bit code the same length. Each five-bit code corresponds to one of the ten (10) digits in the standard arabic numbering system. The reader senses the time taken to scan the space between bars. The logic of the reader is constructed so that a line following a narrow space is registered as a "one" bit, and a wide space is registered as a "zero" bit. This is because a strobe signal examines whether or not the probe is over a line or a space at a predetermined time after a bar has been scanned. If a bar is sensed, a "one" is registered; if a space is sensed, a "zero" is registered.
Murthy, in U.S. Pat. No. 3,700,858, discloses an improvement over the foregoing code in that a pair of lines is substituted for the leading and trailing edge of each bar.
More sophisticated bar codes, such as the Universal Product Code and Codabar, are described in U.S. Pat. Nos. 4,058,708, 3,916,154, 3,886,521, 4,012,716, etc. These codes use timing logic to measure the width of each line and space. In the Universal Product Code, each decimal number is represented by two pairs of vertical bars and spaces within a seven-bit pattern. That is, a decimal four would be represented by 0100011, or a one width space, a one width bar, a three width space, and a two width bar. In scanning these codes, logic which measures the ratios of various components of the character code is used to obtain an accurate reading.
Optical probes for reading bar codes are also known in the art. Alpert, et al., in U.S. Pat. No. 3,761,685, disclose a configuration using a convex lens through which a photosensor gathers light reflected back from two angled lamps positioned in the nose portion of the probe. A frusto-conical baffle prevents light from the lamps from directly impinging on the photosensor.
A scanning pen having a fixed base is disclosed in U.S. Pat. No. 3,238,501. Light from a lamp is directed through a pair of convex lenses. A slit is placed approximately midway between the two lenses. A pair of photosensors is placed adjacent the slit.
A commercially available digital bar code wand is marketed by Hewlett-Packard. It utilizes an optical sensor with a 700 nm visible light source, a photo diode detector, and precision aspheric optics to obtain a resolution of 0.3 mm.
3. Objects of the Invention
It is, therefore, an object of the present invention to provide a low-cost hand-held probe for scanning an optical code.
Another object is to provide a hand-held probe with sufficient resolution to scan an optical code having relatively small spaces between indicia.
It is also an object of the present invention to provide a hand-held probe which emits and receives a large proportion of the light generated by its photoemitter.